Method of shredding fibrous pulp

ABSTRACT

A shredding or fluffing machine for fibrous material such as groundwood, comprising a toothed holding member and a shredding roller with teeth engaging the axial space between the teeth of the holding member with a depth of engagement less than half of the length of the shredding roller, preferably near zero, and a method for operating the machine with a peripheral speed of the shredding roller exceeding 20 m./sec.

United States Patent Inventors Allan Thale Kokkedal; Olav B. Hovstad, Farum, Denmark; Lennart Ivnas, Skarblacka, Sweden Appl. No. 647.088 Filed June 19. 1967 Patented Jan. 13., 1971 Assignee Aktieselskabet Niro Atomizer Soborg, Denmark, and Fiskeby Aktiebolag, Norrkoping, Sweden Priority June 20, 1966 Sweden No. 8396/66 METHOD OF SHREDDING FIBROUS PULP 3 Claims, 7 Drawing Figs.

US. Cl 241/28, 241/243 Int. Cl B02c 4/08, B02c 4/42, B02c 18/06 Field of Search 241/4, 30, 236, 243, 221-225, 227, 230-235, 27, 28, 63, 64

[56] References Cited UNITED STATES PATENTS 3,396,914 8/1968 Liebman 241/243X 2,745,454 5/1956 Fue1ling..... 146/117 93,668 8/1869 Brasil] 241/236 221,744 11/1879 Sanford 241/236X 1,233,514 7/1917 Scott 241/243X 2,236,969 4/1941 Flateboe.... 241/236X 2,306,665 12/ 1 942 Schwarzkopf 241/230X 2,464,774 3/ 1949 Keiper 241/236X FOREIGN PATENTS 461,899 11/1913 France 241/236 Primary Examiner-Robert C. Riordon Assistant ExaminerDonald G. Kelly Attorney-Stevens, Davis, Miller & Mosher ABSTRACT: A shredding or fluffing machine for fibrous material such as groundwood, comprising a toothed holding member and a shredding roller with teeth engaging the axial space between the teeth of the holding member with a depth of engagement less than half of the length of the shredding roller, preferably near zero, and a method for operating the machine with a peripheral speed of the shredding roller exceeding 20 m./sec.

PATENTEU JANIZIBH 8554.453

sum 10F 4 PATENTEU JANI 215m SHEET 4 0F 4 INVENTORS Allan Thole Olav B 'brn Hovsfad Y Lennarf Ivnas B I ATTORNEYS METHOD OF SHREDDING FIBROUS PULP This invention relates to the operation of a machine for shredding fiber goods such as groundwood, sulfate, sulfite or semichemical pulp, w; are the pulp in the shape of a compressed web or flat pieces is passed in between a roller, designated a shredding roller, and a toothed holding or retaining member, where the shredding roller consists of a plurality of toothed discs clamped together with interposed spacing discs of greater thickness and smaller diameter than said toothed discs, or another shape of roller provided with similar toothing, whereas the holding or retaining member consists of a toothed comb with teeth engaging the spaces between said toothed discs or similar toothing'of said shredding roller, or consists of a holding roller with toothings similar to those of the shredding roller and similarly engaged with said toothings of the shredding roller, the latter being adapted for being rotated with respect to said holding member, which in the case of a holding roller, may be arranged for being rotated, for example, at a peripheral speed of the same order of magnitude as the feeding speed of the web.

Such machines are by way of example, used in conjunction with the treatment of fibrous material for the manufacture of paper. Particularly in this case it is to the highest possible degree of importance, to avoid the formation of small fiber bundles, the so-called knots or nodules (in the following the term nodules will be used) in the material, since the nodules will appear as spots or so-called fish eyes" in the finished paper.

The formation of nodules is due to many different reasons, both mechanical as well as chemical, and before as well as after the shredding process, and various methods have been provided'for reducing the effect of the various causes, or for wholly or partially removing said causes, aswell as for removing or dissolving nodules already formed. Since it is not possible with any certainty, to observe the nodules until the paper is finished, it is difficult to safely judge the individual causes for the formation of nodules, or the effects of the measures taken with a view to avoiding such formation.

It is assumed that during the shredding process, nodules already formed may to some extent be broken down. Observations made in conjunction with the development of this invention seem, however, to indicate that this is not correct, or, at any rate, that this is not the primary effect of the shredding on the number of nodules, since it rather seems to be a fact that the shredding process may be a veryess ential reason for the formation of nodules.

Consequently, this invention has for its purpose to provide an arrangement in a machine of the type here concerned, where the risk of nodules being formed during the shredding process is essentially reduced.

According to the invention, this purpose is achieved by the fact that the depth of engagement between the toothings of the shredding roller and those of the holding member is not more than half the length of the shredding roller teeth.

In this way, it is apparent that it is possible to obtain a very considerable reduction in the number of nodules in paper samples made of material where the shredding is effected in the machine according to the invention, as compared to the number of nodules occurring where the shredding or fluffing is effected in the known machines. The explanation of the effect is probably to be looked for in the circumstances that during the shredding process, fibers are pressed down against the bottom of the tooth spaces of the shredding roller. In the known machines, this results in a compression of the fibers in such a way that nodules can be produced, but when using the low depth of engagement provided in this invention, this compression is essentially reduced, so that only few nodules will occur in the finished pulp.

However, in spite of the low depth of engagement, it proves that the shredding will be equally as effective as in the known machines, and in many cases, even so effective, that the machine allows the shredding to be performed as a one-step operation, whereas, in most cases, it has otherwise been possible to use a machine of the type here concerned. only as a coarse shredder, which'is to be succeeded by a fine shredder, the so-called fluffer, in order to attain the desired defibration.

To this may further be added that on account of the low depth of engagement, the muchine, as employed according to the invention, requires less driving power than the known machines of the type concerned.

in many cases it may, according to the invention. be advantageous that the depth of engagement-is less than one'third of the depth of engagement of the shredding roller. preferably near, or equal to zero. This is especially advantageous in connection with the pulps, which, as experience shows, are difficult to shred, such as e.g. sulfite pulp, where it is normally regarded as absolutely necessary to carry out the shredding process as a two step or multistep operation, bl ll where. in spite of all, the shredding or fiuffing has not imparted such properties to the particles as to make it possible to maintain the formation of nodules at a sufficiently low level. Contrary to what was to be expected, a particularly effective shredding is obtained when the depth of engagement is reduced to a very low level, perhaps even as low as zero, and when so proceeding also an extremely low number of nodules is obtained in the finished pulp. A further important fact being that a more uniform particle size is obtained than is possible in the caseof the multistep operation, where during the fluffing step following the coarse shredding carried out in the first step a very wide particle size-distribution occurs.

Although the engagement with the holding member is less critical, it may often be advantageous that the length of tooth of the holding member is at least twice the depth of engagement, preferably about three times the depth of engagement or more. lf so, the engagement with the holding member will, as is the case with the shredding roller, only be a fraction of the length of tooth which, not at least in connection with a stationary holding member, may be of importance.

On account of the low depth of engagement applied accord- I ing to the invention, it may be advantageous to use tooth shapes other than those normally used for such shredders, and thus, it may, according to the invention, be advantageous that the teeth, at any rate, those of the shredding roller, have such shape that, viewed in the direction of movement, the leading tooth flank is, reckoned from the tip of the tooth, forwardly inclined with respect to radius through the tip. In conjunction with the low depth of engagement it appears that such tooth shape results in less formation of nodules than with teeth of the conventionally used shape, where the leading tooth flank is rearwardly inclined with respect to radius.

Further, it is advantageous according to the invention, that in the direction parallel to the axis, the distance between a tooth of the shredding roller and one of the holding member, is 1.5 to 10 mm, preferably 1.5 to 5 mm., as in conjunction with a small distance of about 1.5 mm. a low depth of engagement is used, preferably a depth of engagement equal to or near zero. This distance is of importance for the efficiency of the shredding as well as for the formation of nodules, as a small distance furthers the formation of nodules as well as the efficiency. On account of the low depth of engagement used in the invention, it is possible without any risk to go down to quite a small distance and so obtain a very effective shredding, and still keep the nodule number low.

The method of operating the machine is further characterized in that the shredding roller is rotated at a peripheral speed exceeding 20 m./sec. Although the holding member may be a rotary holding roller, its peripheral speed is in this connection normally of no importance, as in machines of the type here concerned, the speed must, for practical reasons correspond to the rate of feed of material and, consequently, normally lies at a value of less than l mJsec. When rotating the holding roller at an essentially higher speed, it will also be necessary to rotate the shredding roller at a correspondingly higher peripheral speed, since it is the difference in speed that is the deciding factor. The rotation of the shredding roller at the relatively high peripheral speed, in conjunction with the low depth of engagement, increases the efficiency of the shredding process without the high speed causing any essential increase in the formation of nodules, or requiring high driving power.

It is of particular advtntage, notably in the case of pulps difficult to shred, that the shredding roller is rotated at a peripheral speed of to 50 m./sec., and in this case it is according to the invention, advantageous especially for shredding sulfite pulp, that the shredding roller is rotated at a peripheral speed of to m./sec., because even sulfite pulp can, when the roller rotates at such speed, be shredded in a single step and with a minimum formation of nodules.

The invention will be particularly explained below with reference to the accompanying drawings, in which:

FIG. 1 shows schematically a machine of the type dealt with in the invention.

FIG. 2 shows a cross section through line ll-ll in FIG. 1 shown purely schematically.

FIG. 3 is a side view, partially in axial section, of a shredding roller for an embodiment of the machine according to the invention.

FIG. 4 is a tooth disc for the shredding roller shown in FIG. 3.

FIG. 5 is an enlarged and schematical detail for describing the tooth dimensions for the machine according to the invention.

FIGS. 6 and 7 are sectional views of another embodiment of the machine with the FIG. 6 view taken along line 6-6, of FIG. 7.

FIG. 1 and 2 shows a shredding machine highly schematically, consisting of a housing 1, having an inlet passage 2, through which the fiber goods are fed between a toothed holding or retaining member, which in the FIG. is shown in the form of a so-called holding roller 3, and a toothed roller, a socalled fluffing roller 4, disposed in said housing. The fluffs fall down below the rollers and are removed from the housing through a discharge opening 5.

A motor 20 is connected through an endless belt 21, a variable speed drive 22 and a clutch 23 to a shaft 24. The rotation of shaft 24 is transferred by an irreversible worm gear 25, a shaft 26 and over a clutch 27 to an axle 28 on which the holding roller 3 is mounted. The axle is supported by bearings 30 and 30'.

A motor 31 is connected through an endless belt 32 to an axle 33 of the shredding roller 4. The axle is supported by bearings 35 and 35'.

All the bearings 30, 30 nd 35, 35- are mounted on brackets 36 and 37 which are fixed in the housing 1.

The shredding roller 4 for an embodiment of the shredding machine according to the invention, is shown in FIG. 3. This shredding roller consists of a drum 7 mounted on a shaft 6, on which drum provision has been made for toothed annular discs 8 and spacing rings 9 alternately arranged and clamped together by means of end flanges 10 secured to the ends of drum 7 by bolts 11.

Holding roller 3 may be correspondingly designed, and, in the machine, the two rollers should be mounted parallel to each other, with a certain engagement between the toothed annular discs which, consequently, should be axially displaced with respect to each other, so that the teeth of the two rollers engage each others spaces. This is indicated in FIG. 3, which shows some of the two toothings 12 which, e.g. may be toothed annular discs of a holding roller not otherwise shown, said annular discs engaging the spaces between corresponding annular discs 8 of the shredding roller shown. If the holding or retaining member is in the shape of a stationary comb, such comb may be made in a similar way. FIGS. 6 and 7 show such an arrangement wherein the stationary comb consists of a plurality of toothed sectors 40 clamped together with suitable spacers 41 on fixed shaft 42, and disposed in a similar way with respect to the toothings 13 of the shredding roller 4.

FIG. 4 shows part of an annular disc 8 for the shredding roller shown in FIG. 3. This annular disc 8 is at its circumference provided with teeth 13, and for closer explaining the tooth shape used in the embodiment of the invention shown,

an arrow indicates the direction of rotation of the annular disc in the shredding machine. It will be seen that, viewed in the direction of rotation, the leading flank 14 of a tooth 13 is. reckoned from the tip 15, of the tooth, forwardly inclined with respect to the radius R through the tip 15 of the tooth. By this feature the tooth shape differs materially from the tooth shapes normally used in such machines of which a typical shape is indicated in dotted lines, the leading flank 16 of which, viewed in the direction of rotation, is rearwardly inclined with respect to radius through the tip 17 of the tooth.

The trailing flank 18, viewed in the direction of rotation of tooth 13, is in the embodiment shown symmetrical with the leading flank 14 with respect to radius through the tip of the tooth, but its shape is of less importance and has primarily been chosen with a view to obtaining both the required strength and the required length of tooth d.

At the internal circumference of annular disc 8, there are a number of rectangular notches 9 which in combination with similarly shaped keys and keyways in drum 7, serve to prevent the annular discs from rotating with respect to the drum.

The tooth shape of holding member 3, may be chosen rather arbitrarily, and it will, therefore, if the member is in the shape of a roller, for productional reasons be advantageous to use toothed annular discs for this roller of the same shape and dimensions as those used for shredding roller 4.

FIG. 5 shows the engagement between the toothed annular discs of the shredding roller and toothings 12 of the holding member.

The length of tooth of the shredding roller is designated by d, whereas the depth of engagement of the two toothings is designated by i, and the free space between the successive toothings of the holding member 3 and the shredding roller 4 is designated by a.

The depth of engagement 1 is, according to the invention not more than half the length of tooth d, and is in FIG. 4 shown in the order of about one third d, whereas, according to the invention it may be as low as zero. As is the case in the known shredders or fluffers, distance a must be sufficiently large to prevent the toothings from getting jammed in the material, but as a consequence of the low depth of engagement, the distance a may, according to the invention, be of a very low order. The distance a is preferably chosen to be between 3 and 5 mm., but it may be still lower, for example, as low as 1.5 mm., but if so, the depth of engagement should be near zero. A small distance a will most often result in a very high efficiency of the shredding process, and as a result of the low depth of engagement, the risk of nodules formation, which is highly enhanced when distance a is small, is not present, and it appears, moreover, that even the use of a diminishing depth of engagement does not deteriorate the efficiency to any appreciable extent.

The depth of engagement with respect to the length of tooth of the holding member is, as a rule, less critical, but most often this length of tooth may advantageously be so chosen as to maintain the depth of engagement to the length of tooth ratio within the same limits as those applying to the shredding roller.

For the toothed annular discs it would, for example, be possible to use relatively soft steel, which is adequately surface-hardened, for example, case hardened. If so, it is posible without any difficulty, to obtain the required wear properties as well as the required tensile strength of the teeth. With a tooth length d, of about 15 mm., a thickness of 2 to 3 mm. could suitably be used, and with spacing rings 9 of 10 mm., the distance a will be 3.5 to 4 mm., which in many cases will give a particularly excellent result.

Shredding roller 4 is driven by driving means not shown. If the holding member is also a rotary roller, a single drive motor may be used for the two rollers, but as the shredder, according to the invention most often will use a shredding roller rotating at a very considerable speed,'whereas, the holding roller is to rotate at a relatively low speed, it will often be advantageous, with a view to avoiding too high ratios, to use a separate drive motors for the two rollers.

When a rotary holder is used, its peripheral speed should, as a rule, correspond to the rate of feed of the material. If, for example, the material is fed to the machine in the shape of a con-. tinuous web, e.g. delivered from a dehydration press, the rate of feed will normally lie about 0.5 mjsec. lf this roller rotates too fast, such continuous web will be torn apart so that the operation of the machine will become irregular. The object of the holding roller is substantially to maintain the material pressed against shredding roller 4, and to advance said material between the rollers at an appropriate speed. The shredding roller 4, on the other hand, has to be driven at a higher speed and, consequently, a certain moment of rotation is transferred to the holding roller, tending to cause it to rotate at a higher speed than desired. Consequently, measures have to be taken to ensure the desired speed of rotation of the holding roller, which, for example, can be done by the roller being driven through an irreversible worm gear, which will brake the roller towards torques outside the worm.

According to the invention, shredding roller 4, is preferably driven at a speed of 25 to 30 m./sec. If this speed is reduced to a value essentially lower than 20 m./sec., for example, lower than m./sec., the efficiency of the shredding process is considerably reduced, whereas, a speed essentially above 50 m./sec., must be regarded as inexpediently high, because the reduction of the nodule number resulting from an increase of the speed within the range stated in connection with this infiber goods for other purposes, because by means of this machine, one obtains, in addition to the reduced formation of nodules, an essentially increased efficiency of the Shredding process and less power consumption, both of which factors are, as a matter of fact, of independent significance, and are, therefore, also of importance in such case where the formation of nodules is of less importance.

1 claim:

1. A method of shredding fibrous articles such as groundwood, and compressed webs and flat pieces of sullite and semichemical pulp, comprising passing said fibrous articles between a shredding roller rotating at a peripheral speed exceeding 20 meters per second and a holding roller rotating at a peripheral speed of from 0 meters per second to the rate of feed of said'fibrous articles while subjecting same to the action of a plurality of laterally spaced interdigitating toothed discs carried by said rollers, the depth of engagement between the teeth of the discs of the shredding roller and those of the holding roller being not more than half the length of the teeth of the shredding roller.

2. The method of claim 1 wherein the shredding roller is rotated at a peripheral speed of from 20 to 50 m./sec.

3. The method of claim 2 wherein the shredding roller is rotated at a peripheral speed of from 25 to 40 m./sec 

2. The method of claim 1 wherein the shredding roller is rotated at a peripheral speed of from 20 to 50 m./sec.
 3. The method of claim 2 wherein the shredding roller is rotated at a peripheral speed of from 25 to 40 m./sec. 